1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor, a display device including the semiconductor device, and a manufacturing method thereof.
2. Description of the Related Art
Various metal oxides are used for a variety of applications. Indium oxide is a well-known material and is used as a light-transmitting electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. As metal oxides exhibiting semiconductor characteristics, for example, tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like can be given. References disclose a thin film transistor in which such a metal oxide exhibiting semiconductor characteristics is used for a channel formation region (Patent Documents 1 to 4, and Non-Patent Document 1).
As the metal oxides, not only single-component oxides but also multi-component oxides are known. For example, homologous compound, InGaO3(ZnO)m (m is natural number) is known as a multi-component oxide including In, Ga and Zn (Non-Patent Documents 2 to 4).
Further, it is confirmed that such an oxide semiconductor made of In—Ga—Zn-based oxide is applicable to a channel layer of a thin film transistor (Patent Document 5 and Non-Patent Documents 5 and 6).
In a conventional technique, amorphous silicon or polycrystalline silicon has been used for a thin film transistor (a TFT) provided for each pixel of an active matrix liquid crystal display. However, in place of these silicon materials, attention has been attracted to a technique for manufacturing a thin film transistor including the aforementioned metal oxide semiconductor. Examples of the techniques are disclosed in Patent Document 6 and Patent Document 7, in which a thin film transistor is manufactured with zinc oxide or an In—Ga—Zn—O-based oxide semiconductor for a metal oxide semiconductor film and is used as a switching element or the like of an image display device.